This invention relates to a gas component detector which detects the concentration variation of gas components such as O.sub.2 (oxygen), CO (carbon monoxide) and HC (hydrocarbon) in the exhaust gas of an internal combustion engine as a variation of the whole atmosphere of the engine.
According to one method for detecting the air-fuel ratio of mixture supplied to the internal combustion engine, a gas component detecting element is used, which is formed by metal oxide such as titanium oxide sensitive to the concentration of exhaust gas components and shows a value of electric resistance corresponding to the concentration of exhaust gas components. There has been an apparatus for detecting the air-fuel ratio of mixture, in which the above-mentioned gas component detecting element is connected in series with a fixed reference resistor and a variation of electric resistance value is taken from a connection point between the detecting element and the resistor to compare the resistance value with a reference voltage. However, such a prior art apparatus can not make accurate detection of an air-fuel ratio due to the following reasons. That is, when the temperature of exhaust gas varies, the electric resistance of the gas component detecting element also varies, so that even if there is no variation of exhaust gas components the voltage at the connection point between the gas component detecting element and the fixed reference resistor varies. Furthermore, the prior art apparatus is defective in that the electric resistance vs. temperature characteristic of the gas component detecting element varies with age, losing the capability of proper measurement of exhaust gas components.